AUTHOR=Hanson-Drury Sesha , Patni Anjali P. , Lee Deborah L. , Alghadeer Ammar , Zhao Yan Ting , Ehnes Devon Duron , Vo Vivian N. , Kim Sydney Y. , Jithendra Druthi , Phal Ashish , Edman Natasha I. , Schlichthaerle Thomas , Baker David , Young Jessica E. , Mathieu Julie , Ruohola-Baker Hannele TITLE=Single cell RNA sequencing reveals human tooth type identity and guides in vitro hiPSC derived odontoblast differentiation (iOB) JOURNAL=Frontiers in Dental Medicine VOLUME=4 YEAR=2023 URL=https://www.frontiersin.org/journals/dental-medicine/articles/10.3389/fdmed.2023.1209503 DOI=10.3389/fdmed.2023.1209503 ISSN=2673-4915 ABSTRACT=

Over 90% of the U.S. adult population suffers from tooth structure loss due to caries. Most of the mineralized tooth structure is composed of dentin, a material produced and mineralized by ectomesenchyme derived cells known as odontoblasts. Clinicians, scientists, and the general public share the desire to regenerate this missing tooth structure. To bioengineer missing dentin, increased understanding of human tooth development is required. Here we interrogate at the single cell level the signaling interactions that guide human odontoblast and ameloblast development and which determine incisor or molar tooth germ type identity. During human odontoblast development, computational analysis predicts that early FGF and BMP activation followed by later HH signaling is crucial. Here we generate a differentiation protocol based on this sci-RNA-seq analysis to produce mature hiPSC derived odontoblasts in vitro (iOB). Further, we elucidate the critical role of FGF signaling in odontoblast maturation and its biomineralization capacity using the de novo designed FGFR1/2c isoform specific minibinder scaffolded as a C6 oligomer that acts as a pathway agonist. Using computational tools, we show on a molecular level how human molar development is delayed compared to incisors. We reveal that enamel knot development is guided by FGF and WNT in incisors and BMP and ROBO in the molars, and that incisor and molar ameloblast development is guided by FGF, EGF and BMP signaling, with tooth type specific intensity of signaling interactions. Dental ectomesenchyme derived cells are the primary source of signaling ligands responsible for both enamel knot and ameloblast development.